Heat exchangers such as the steam generators of a pressurized water nuclear reactor have a tube bundle constituted by a very large number of small diameter tubes positioned vertically within a generally cylindrical bundle envelope located within the very thick, outer, rigid pressure envelope of the steam generator.
The pressurized water of the nuclear reactor circulates within the small diameter tubes and the water to be vaporized is introduced into the envelope of the bundle where it comes into contact with the outer surface of the tubes. The steam is recovered on the upper portion of the bundle envelope and is then generally dried in steam-water separators located in the outer envelope of the steam generator above the envelope of the tube bundle.
Steam generators constitute very high units, in which coaxial envelopes are arranged with a generally small, radial spacing.
It is known to use spacer plates into which pass the tubes of the bundle, distributed in accordance with the bundle height, in order to maintain the tubes in reciprocally fixed radial positions. These spacer plates are interconnected by vertical ties, the assembly being placed within the bundle envelope.
It is therefore important to support the different coaxial envelopes of the steam generators and the complete bundle by spacer plates in radial directions, so as to avoid relative displacements and shocks between these envelopes and the bundle in the case of external stresses such as those which accompany an earthquake.
This radial holding or supporting is obtained by abutments fixed to the envelope of the bundle level with the spacer plates, several abutments being provided for each spacer plate. These abutments are then evenly distributed over the periphery of the spacer plates.
Such a holding or supporting device is known from FR-A-2 511 491. It is constituted by parts having a thickness exceeding the thickness of the bundle envelope and having tapped holes into which can be screwed the threaded studs, whose end projecting into the space between the bundle envelope and the outer, rigid envelope bears against the inner surface of the outer envelope. The bearing action of these abutments is brought about following adjustment of the studs, by the introduction of wedge-like shims between the outer edge of the spacer plates and the inner surface of the bearing device directed towards the bundle.
Such abutments suffer from the disadvantage of occupying a large part of the width of the space between the bundle envelope and the outer envelope and consequently significantly reduce the passage cross-section for the water to be vaporized circulating in the space, and without providing a perfect seal. These abutments also have the disadvantage of requiring the introduction of shims into notches machined on the peripheral part of the spacer plates. These notches lead to a corresponding reduction of the distance between the peripheral tubes of the bundle and the edge of the spacer plates. If an adequate distance is to be maintained between the peripheral tubes and the plate, it is then necessary to reduce the number of tubes in the bundle. In addition, the abutments must have shapes which do not facilitate their fixing by welding in the wall of the bundle envelope.
Other devices for the radial holding of the bundle envelope and the spacer plates of a steam generator are disclosed in FR-A-2 562 996 and 4,503,903, 4,583,584, 4,690,206 and 4,768,582. None of these devices is entirely satisfactory. Their assembly and installation are generally complicated by the use of shims for some of them. Certain of these devices do not provide an adequate bearing surface for satisfactorily supporting the spacer plates.